Tool made from plastic

ABSTRACT

The invention relates to tools ( 11, 12 ), made from plastic and a material with slide bearing properties inlaid in the plastic, whereby the plastic tools further comprise a component of inlaid aluminium. Said plastic tools are suitable for the moulding, in particular the deep-drawing of metallic workpieces ( 10 ), such as for example components of automobiles. The tools have a high pressure-resistance and wear resistance and permit deep-drawing with essentially small amounts of, or no, lubricants as a result of said slide bearing properties.

The present invention relates to a tool made of a plastic and a materialwith lubricant properties embedded in the plastic. Tools within themeaning of the present invention are, in particular, forming tools, suchas deep-drawing tools for the forming of metal components, such asautomobile components.

Tools made of steel or gray cast iron are conventionally used fordeep-drawing. For some time, plastics, such as plastics containingmetallic fillers, have also been used for deep-drawing. An advantage ofthese plastics is that they are more cost-effective materials. However,it has been found that, for certain applications, such plastic-basedtools can be used as deep-drawing tools not at all, or can only be usedwith restrictions. This is especially applicable to deep-drawingapplications in which workpieces must be formed in large numbers, sothat the tool is subject to substantial wear. Tools made of plasticsalso exhibit insufficient resistance to pressure in these applicationcases.

DE 93 18 272.4 U1 describes a tool for the non-cutting forming ofworkpieces, with the tool per se being made of a metallic material,especially gray cast iron, while a guide component of the tool, whichhas a slide face, is made of a duroplastic with a fiber or wovenmaterial insert and embedded laminar graphite. This is done to improvethe lubricant properties and reduce wear.

The object of the invention lies in providing a tool made of plasticwhich, on the one hand, exhibits favorable lubricant properties and, onthe other hand, also exhibits improved wear properties and highresistance to pressure.

This object is attained by providing a tool according to the inventionhaving the features of the principal claim. According to the invention,the synthetic tool contains a component of embedded aluminum to achievegreater resistance to pressure and wear resistance, and, furthermore, anembedded material with lubricant properties, so that the toolessentially possesses a self-lubricating capacity. As a result, the useof an additional lubricant in the region between the forming tool andthe workpiece to be formed is generally unnecessary. Experiments haveshown that the serviceable life of the tool can be significantlyimproved by the embedded materials. Examples of possible materials withlubricant properties are graphite or molybdenum sulfide. The use ofgraphite powder is especially preferred. Aluminum can be contained inthe synthetic tool as a filler, for example, in the form of aluminumpowder or large-grained aluminum particles. Tools of this nature arepreferably made with a correspondingly composed cast resin or from ablock material.

According to a preferred embodiment of the invention, the tool containsa weight component of more than approximately 50% aluminum filler. Theweight component of aluminum filler in the plastic mass used to producethe tool can be several times that of the plastic component. This weightcomponent is preferably at least about 60%, preferably about 70%aluminum filler, preferably aluminum powder, relative to the totalweight of the plastic compound.

The weight component of the material with lubricant properties embeddedin the plastic is generally lower than the plastic component and/or thealuminum component of the plastic compound. The tool preferably containsa weight component of at least 20% to approximately 50% graphite powderrelative to the weight component of the plastic contained in the tool,i.e.,. not relative to the total weight of the plastic compound, butrelative to the pure plastic component. The weight component of thegraphite, relative to the total weight of the material of which the toolis made, is preferably at least approximately 3% to approximately 15%graphite. The weight ratio between the graphite component and thealuminum component is preferably between 1:15 and 1:6.

Within the scope of the present invention, the production of tools forforming processes is preferred, especially of deep-drawing tools made ofthe plastic compound of the type stated above. They can be dies orhold-down devices for the deep-drawing of metal parts, for example.Embedding the material with lubricant properties prevents, during thedeep-drawing of a metal plate, for example, which is stressed in thisprocess in a tensile direction perpendicular to the direction of motionof the deep-drawing tool, particles, especially filler particles, frombeing torn out of the plastic matrix, resulting in cracks in the tool.It has already been mentioned that graphite in the form of graphitepowder can be embedded in the plastic, as a material with lubricantproperties. The use of graphite powder with a particle size betweenapproximately 50 μm and approximately 250 μm has proven to be especiallyadvantageous.

The tools according to the invention can essentially be made entirely ofplastic having the stated embedded material; in other words, they areconsistently made of a homogeneous plastic compound, therebydistinguishing them from the tools described in DE 93 18 272.4 U1mentioned at the outset, in which only a front layer of the tool,referred to as a guide component, is made of a plastic with certainlubricant properties.

The features specified in the subclaims relate to preferred embodimentsof the object attained according to the invention. Further advantages ofthe invention can be found in the following detailed description.

In the following, the present invention will be explained in greaterdetail, using exemplary embodiments with reference to the attacheddrawings, which show

FIG. 1 a highly schematically simplified perspective view to explain adeep-drawing process by means of a tool according to the invention;

FIG. 2 a second schematically simplified view to explain thedeep-drawing process;

FIG. 3 a diagram, which shows the change in the modulus of elasticitywhen plastics with various fillers are used;

FIG. 4 a male die for deep-drawing valve covers for motors inperspective view;

FIG. 5 the corresponding female die for deep-drawing valve covers with amale die according to FIG. 4;

FIG. 6 valve covers deep-drawn by means of the male and female diesshown in FIGS. 4 and 5.

First reference is made to FIG. 1. The drawing shows, in a highlyschematically simplified perspective view, an array of tools fordeep-drawing a sheet metal component 10. An upper tool part 1 1 isprovided for forming the sheet metal component 10 in a deep-drawingprocess, as well as a lower tool part 12 in the form of a female diethat accepts the upper tool part 11. The upper tool part 11 is made of aplastic of the type according to the invention, which contains embeddedaluminum particles 13, as well as embedded graphite powder 14, toachieve a self-lubricating effect during forming of the sheet metalcomponent 10.

The upper tool part 11 was made with a cast resin composed of plastic,aluminum powder as filler, and graphite powder. In this process, 1 kg ofplastic, 3 kg of aluminum powder and 200 g of graphite powder were usedto produce a compound of this material totaling 4.2 kg. The particlesize of the graphite powder varied between 50 and 250 μm. The plastictool had very good lubricant properties and a 40% increase in resistanceto pressure. The cracking that occurs in the front layer of tools madeof other plastics with conventional fillers, such as sand and iron,which is caused by filler particles being torn out of the underlyingmatrix of the plastic compound during the deep-drawing process, did notoccur when using tools made of the plastic according to the invention.

It was found that the deep-drawing tools made of the abovementionedplastic compound are suitable for forming workpieces in higher numbers,such as up to 100,000 or more.

FIG. 2 illustrates the forces acting on the tool that cause the statedcracking during deep-drawing with materials lacking adequate lubricantproperties. In a highly schematically simplified sectional view, anupper tool part 11 is shown which, according to the invention, was madeof a full cast material composed of a plastic of the inventioncontaining aluminum and graphite powder as fillers. The lower tool part15 was also cast from the plastic compound of the invention. Beforeentering the deep-drawing process, the sheet metal component 10 to beformed is located in the gap 16 between the upper tool part 11 and thelower tool part 15. During deep-drawing, the sheet metal component 10 tobe formed is deformed, with forces acting in the direction of the arrow17, perpendicularly to the direction of motion. As a result, the frontsurfaces 18, 19 of the two tools 11, 15 are subjected to shearingaction. The graphite powder embedded in the plastic of the tools 11, 15provides a lubricant effect and favorable sliding properties in theinterface zone among the front surfaces 18, 19, the tools 11, 15 and thedeep-drawn sheet metal component 10.

FIG. 3 illustrates the percentage change in the modulus of elasticity oftools made of various plastics, which was determined on the basis ofcompression tests within the scope of the invention. The modulus ofelasticity of a plastic filled only with aluminum is shown in column 20in the far left of the diagram, and is assigned a value of 100 as arelative reference quantity for the other plastics. The relative valueof the modulus of elasticity for a PTFE filled with aluminum is shown inthe second column from the right, which is identified by referencenumber 22, and it is evident that this value only amounts to about 60%of that of the plastic shown in column 20 in FIG. 3. For purposes ofcomparison, the moduli of elasticity for two plastics manufacturedaccording to the invention are shown in FIG. 3. Column 23, at far rightin the figure, shows the value for a plastic filled with aluminum andMoS₂ as the lubricant. It is evident that the modulus of elasticity ismore than 20% greater than that of the plastic filled with aluminum,which is shown in column 20. The relative value of the modulus ofelasticity for a plastic filled with graphite and aluminum is shown incolumn 21 (second from left in the figure). As is evident in the figure,this value is 40% higher than the modulus of elasticity for a plasticfilled with aluminum, as shown in column 20 at the far left of thefigure. The value shown in column 21 in FIG. 3 was reached by adding 20%graphite power to an aluminum-filled plastic, for which the value isshown in column 20. For deep-drawing experiments, a deep-drawing tool30, shown in perspective in FIG. 4, was used to design, lay out andmanufacture valve covers for a three-cylinder motor. FIG. 4 shows theunderside of a deep-drawing die for valve covers 30, which is made witha plastic according to the invention. Deep-drawing experiments wereconducted with this tool 30. Based on these experiments, it wasdetermined that dimensional accuracy, serviceable life and theself-lubricating effect were significantly improved in comparison totools made with other plastics. Tools made with conventional plasticswere worn after a short period of time. As a result of the embedding ofonly about 20% graphite powder in a plastic filled with aluminum powder,significantly better friction and wear conditions were achieved with thetool 30 shown in FIG. 4. As is evident in FIG. 4, the deep-drawing diefeatures two characteristic forming elements 31, 32 to produce thedepressions and raised areas typical of the shape of the valve cover.

FIG. 6 shows examples of valve covers made of various materials, whichwere manufactured by means of the deep-drawing tool 30 shown in FIG. 4.The valve covers 40, 41, 42 shown in FIG. 6 were manufactured by formingsheets of titanium, aluminum and galvanized steel, each having amaterial thickness of 1 mm. The characteristic formed regions, namelythe flat cylindrical depression 43 (or elevation, when the deep-drawnvalve covers 41 shown in FIG. 6 are viewed from below), are easilyrecognizable in the depiction shown in FIG. 6. This formed region 43 canbe matched to the forming element 32 of the deep-drawing tool 30 shownin FIG. 4. Accordingly, the formed region 44 can be matched to theforming element 31 of the deep-drawing tool 30 shown in FIG. 4. When thevalve cover shown in FIG. 6 was deep-drawn with the tool 30 according tothe invention, it was possible to achieve very good results with allthree materials, sheet titanium, sheet aluminum, and galvanized sheetsteel.

FIG. 5 shows the female die 50 corresponding to the deep-drawing die 30shown in FIG. 4, for the production of valve covers 40, 41, 42, as shownin FIG. 6. The die 30 is lowered into the deep-drawing female die 50shown in FIG. 5. The shape of the female die 50, approximatelyrectangular and rounded at the edges, which corresponds to the die 30,is recognizable in FIG. 5. Also recognizable is the formed region 51,which matches the approximately cylindrical forming element 32, as adepression in the deep-drawing tool serving as a female die 50. Thefemale die 50 shown in FIG. 5 was also made with the plastic of theinvention, which contains aluminum and graphite powder.

The advantages of the plastic tools made with the materials according tothe invention, in comparison to conventional steel tools, lie, forexample, in the material costs, which are reduced by up to about 70%.The plastics used to manufacture the tools are more easily machined,reducing the use of machinery in production of the tools. Energy andoutput requirements during the machining work required to produce thetools can be reduced by 65%, for example. The break-in time is alsoshorter than with steel tools, by up to 60%, for example. The use ofplastics according to the invention for production of the tools leads toa substantial reduction in weight of up to 60%, for example, and thus toa reduction in loads on crane equipment. The tools can be modified moreflexibly and cost-effectively, thereby achieving a high degree of cost,time, and energy savings. The tools are also suitable for recycling,because they can be fully recycled as filler material in the productionof new plastic tools, thus eliminating disposal costs.

The elastic behavior of the plastics results in improvement of thequality of the formed workpieces. Embedding graphite in the plastic ofthe tools produces a self-lubricating effect on the contact surfaces ofthe tool. If it is even necessary to additionally use liquid lubricantsduring forming, the amount of lubricant necessary can be significantlyreduced, such as by approx. 3 g/m². The frictional conditions duringdeep-drawing are improved by incorporating graphite powder into theplastic. As a result of the elimination of or reduction in liquidlubricants during deep-drawing, dirt accumulation in the work area issignificantly reduced, thereby benefiting the environment.

LIST OF REFERENCE CHARACTERS

10 Sheet metal component

11 Upper tool part

12 Lower tool part

13 Aluminum particle

14 Graphite powder

15 Lower tool part

16 Gap

17 Arrow

18 Front surface

19 Front surface

20 Column

21 Column

22 Column

23 Column

30 Deep-drawing tool

31 Forming element

32 Forming element

40 Valve cover

41 Valve cover

42 Valve cover

43 Depression

44 Forming region

50 Deep-drawing female die

51 Deep-drawing region

1-14. (Canceled).
 15. A tool made from a plastic compound, wherein saidcompound comprises a plastic component having embedded therein amaterial with lubricant properties and a component of aluminum.
 16. Thetool according to claim 15, wherein the component of aluminum comprisesa filler selected from the group consisting of aluminum powder andaluminum particles.
 17. The tool according to claim 15, wherein thematerial with lubricant properties is graphite or molybdenum sulfide.18. The tool according to claim 17, wherein the material with lubricantproperties is graphite.
 19. The tool according to claim 18, wherein thegraphite is graphite powder.
 20. The tool according to claim 15, whereinthe tool is made with a block material or a cast resin.
 21. The toolaccording to claim 16, wherein the tool contains a weight component ofmore than approximately 50 percent aluminum filler.
 22. The toolaccording to claim 16, wherein the aluminum filler is at leastapproximately 60 percent by weight relative to the total weight of theplastic compound.
 23. The tool according to claim 22, wherein thealuminum filler is at least approximately 70 percent by weight relativeto the total weight of the plastic compound.
 24. The tool according toclaim 22 or 23, wherein the aluminum filler is aluminum powder.
 25. Thetool according to claim 18, wherein the graphite is at leastapproximately 20 to approximately 50 percent by weight relative to theweight of the plastic component of the plastic compound.
 26. The toolaccording to claim 18, wherein the graphite is at least approximately 3to approximately 15 percent by weight relative to the plastic compound.27. The tool according to claim 25 or 26, wherein the graphite isgraphite powder.
 28. The tool according to claim 18, wherein the weightratio of the graphite component to the aluminum component is betweenapproximately 1:15 and approximately 1:6.
 29. The tool according toclaim 28, wherein the graphite and the aluminum are in powder form. 30.The tool according to claim 19, wherein the graphite powder has aparticle size between approximately 50 μm and approximately 250 μm. 31.The tool according to claim 15, wherein the tool is a forming tool. 32.The tool according to claim 15, wherein the tool is a deep-drawing tool.33. The tool according to claim 15, wherein the tool is a die, ahold-down device or a female die for the deep-drawing of metalcomponents.
 34. A process for the formation of a part comprising thesteps of obtaining a workpiece and subjecting the workpiece to theaction of a tool according to claim
 15. 35. A process according to claim34, wherein the process is a deep-drawing process, and the workpiece issheet metal.